FR2952929A1 - PROCESS FOR PRODUCING HYDROGEN FROM REGENERABLE NON-STOICHIOMETRIC METAL SULFIDES - Google Patents

Abstract

The present invention relates to a process for producing hydrogen from a feedstock comprising hydrogen sulphide, wherein said feedstock is contacted with a material comprising at least one initial metal sulphide so as to produce hydrogen and a converted metal sulfide, said initial metal sulfide being a non-stoichiometric sulfide of a Group VIIIB metal of the Mendeleyev Periodic Table.

Description

The present invention relates to the production of hydrogen from a hydrogen sulfide (H2S) feedstock and a non-stoichiometric metal sulfide.

Hydrogen sulfide (H2S) is a highly toxic compound found in many natural gases. It is also found in refinery gases, where it is generally derived from decomposition reactions of organic sulfur compounds naturally present in crude oils. In particular, hydrogen sulphide is produced in large quantities during hydrodesulfurization operations. These operations make it possible to lower the sulfur content of the petroleum fractions by a treatment with hydrogen in the presence of appropriate catalysts.

It is conventional, both in the refinery and in the production of natural gas, to extract the H2S present in the gases by washing with a suitable solvent, for example an amine-based solution. This solvent is then regenerated, generally by heating, which then produces a gas, said acid, rich in H2S. In refinery such acid gas usually contains more than 90% H 2 S with minor amounts of CO2, water vapor and hydrocarbons (methane and other heavier hydrocarbons).

Given the toxicity of H2S, this gas can not be released to the atmosphere. In addition, its combustion would generate considerable amounts of S02 and SO3, pollutant compounds which are also sought to minimize releases to the atmosphere. The most common method of treating these acid gases is to admit them into a unit called the Claus unit. This unit makes it possible to convert H2S into elemental sulfur, a non-polluting compound that can easily be transported and marketed, for example for the production of sulfuric acid.

The conversion of H2S to hydrogen and sulfur is another conversion method that is being explored. This transformation makes it possible to produce hydrogen, a gas with a high added value, which is also highly demanded by various refining operations for crude oils (hydrotreatments).

The H2S can be directly thermally decomposed according to the reaction: H2S - ~ H2 + S0 H293 = +79.9 kJ / mole This reaction has thermodynamic limits and to reach yields of 50% in hydrogen, 1500 ° C is required. In addition, the presence of impurities penalizes the yield of the reaction.

Various processes have been developed to attempt to produce hydrogen industrially from H2S. One can, for example, mention the process based on the dissociation of H2S electrolytically, such as that developed by the company Idemitsu Kosan. Although this process makes it possible to obtain almost total conversion of H2S to elemental sulfur and hydrogen, the use of electricity as the sole source of energy leads to a high operating cost.

It is also the use of electricity as the sole source of energy, which penalizes the process by plasmalysis developed by the Kurchatov Russian Institute. The "Hysulf" process developed by Marathon Oil makes it possible to obtain hydrogen using only thermal energy, thanks to the use of hydrogenated organic compounds by H2S in a first step, Then, it is generally accepted that during such reduction-oxidation cycles the organic compounds tend to be degraded, therefore processes based on this type of reaction often lead to relatively high operating costs due to the addition of chemicals needed to compensate for secondary degradation reactions.

The thermal cracking path developed by the Alberta Sulfur Research Laboratory ASRL also allows the use of thermal energy only to dissociate H2S. This energy is directly supplied by the flame of a thermal stage of the Claus process. The conversion yields obtained, however, are relatively low (limited to around 35%); this mainly for two reasons: - the theoretical limitations due to the thermodynamic equilibrium between H2S, H2 and elemental sulfur, the dissociation of the H2S only becoming important at very high temperature (1100 ° C. and beyond), the difficulty in rapidly cooling the high temperature mixture containing hydrogen. Indeed during cooling, hydrogen and elemental sulfur formed at high temperature tend to recombine in H2S very quickly.

To date no method has apparently been the subject of a large-scale industrial implementation, generally because of insufficient conversion rates or high operating costs.

More recently, the Applicant has developed a new process for producing hydrogen from H2S based on the use of metal oxides. This process described in application WO-A-2009/090316 is based on a reaction for the production of hydrogen from a metal oxide and on a regeneration reaction of the metal oxide. These reactions are detailed below: (a) production reactions: M3O4 + 6 H2S -> 3 MS2 + 4 H2O + 2 H2 or M2O3 + 4 H2S -> 2 MS2 + 3 H2O + H2 (b) reactions of regeneration: The regeneration is carried out by calcination with oxygen or air in order to regenerate the initial oxide according to the following reactions: 3 MS2 + 8 02 -> M3O4 + 6 SO2 2 MS2 + 5,5 02 -> M2O3 + 4 SO2 The process described in WO-A-2009/090316 has several disadvantages. It produces SO2 which must be recycled according to methods well known to those skilled in the art. The treatment of SO2 increases the production costs of the process. In addition, the production reactions (a) have a hydrogen yield of between 25 and 33% and the majority of the reaction products are water. Finally, the regeneration reactions (b) can be problematic because there is a risk of sulphate formation.

There is, therefore, still a need for a process which makes it possible to produce hydrogen from hydrogen sulfide with good yield, which is industrially adaptable and inexpensive.

The present invention proposes to remedy the aforementioned problems by a process for producing hydrogen from a feedstock comprising hydrogen sulphide, wherein said feedstock is brought into contact with a material comprising at least one initial metal sulphide to produce hydrogen and a converted metal sulfide, said initial metal sulfide being a non-stoichiometric sulfide of a Group VIIIB metal of the Mendeleev Periodic Table. The production process according to the invention uses non-stoichiometric metal sulphides, that is to say having gaps either at the level of the metal or at the level of the sulfur.

The metal of said initial metal sulfide used in the process according to the invention is selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium and nickel.

In a particular version of the process according to the invention, the metal of said sulphide is iron and is carried out at a temperature of between 20 ° C. and 500 ° C., preferably between 50 ° C. and 500 ° C., and even more preferably 100 ° C. ° C and 450 ° C.

Advantageously, the iron sulfide is chosen from the group consisting of mackinawite, pyrrhotite and smythite. Preferentially, the iron sulphide is pyrrhotite and is carried out at a temperature of between 100 ° C. and 450 ° C. In another particular version of the process according to the invention, the metal of said sulfide is rhodium and is operated at a temperature between 20 ° C and 800 ° C, more preferably between 50 ° C and 700 ° C, even more preferred between 150 ° C and 500 ° C.

In another particular version of the process according to the invention, the metal of said sulphide is molybdenum and is carried out at a temperature of between 20 ° C. and 800 ° C., more preferably between 50 ° C. and 700 ° C. more preferred between 150 ° C and 500 ° C.

In another particular version of the process according to the invention, the metal of said sulphide is cobalt and is carried out at a temperature of between 20 ° C. and 1000 ° C., more preferably between 100 ° C. and 600 ° C. more preferred between 150 ° C and 500 ° C.

In another particular version of the process according to the invention, the metal of said sulphide 25 is nickel and is carried out at a temperature of between 20 ° C. and 500 ° C., more preferably between 30 ° C. and 450 ° C., moreover more preferred between 100 ° C and 450 ° C.

In another version of the process according to the invention, the material comprises between 0.01% and 100% by weight of initial metal sulphide, preferably between 15% and 100% by weight, preferably between 15% and 90% by weight, of more preferably between 50% and 100% by weight, more preferably between 90% and 100% by weight of initial metal sulfide.

In another version of the process according to the invention, the metal content of the initial metal sulphides supported is between 0.01% by weight and 15% by weight, preferably between 0.01% by weight and 7% by weight. still more preferably 0.01% and 5% by weight. The process according to the invention may comprise contacting the feed with the metal sulphide with one of the following means: a contacting column, a reactor fixed bed, a moving bed reactor.

In one version of the process according to the invention, the initial metal sulphide is contained in an enclosure comprising at least one membrane wall which is permeable to hydrogen and the migration of hydrogen through the membrane is caused by pressure difference or by difference in hydrogen concentration.

In another version of the process according to the invention, after the chemical reaction step, a separation step is carried out in which the hydrogen is separated by means of a membrane that is permeable to hydrogen in order to obtain a depleted effluent. hydrogen and a stream rich in hydrogen.

Advantageously, at least two sequences are carried out comprising the chemical reaction step followed by the separation step.

The membrane used in the process according to the invention may comprise a dense film comprising a polymer whose glass transition temperature is greater than 150 ° C. or a dense film comprising palladium and copper.

In another version of the process according to the invention, a step of capturing unconverted H2S is carried out after the chemical reaction step in order to obtain a flow rich in hydrogen. In another version, the process according to the invention may comprise, in addition, a step in which the transformed metal sulphide is regenerated by calcination at a calcination temperature of between 100 and 1000 ° C.

Advantageously, the regeneration step of the metal sulphide converted by calcination can be carried out in the presence of an inert gas.

The process according to the invention makes it possible to obtain hydrogen production yields higher than the yields obtained with the processes of the prior art, under simplified reaction conditions (low temperatures, between 100 ° C. and 500 ° C.). and without water formation. The process according to the invention is more economical, more secure and less polluting. The process according to the invention is particularly advantageous since it makes it possible to produce hydrogen with a high yield over several consecutive days. Other features and advantages of the invention will be better understood and will be clearly apparent on reading the description given below with reference to the drawings among which Figure 1 shows an embodiment of the invention by means of a stirred reactor. FIG. 2 represents a second embodiment of the invention with a fixed bed reactor. FIG. 3 schematizes a third embodiment of the invention by means of a membrane reactor. Figures 4 and 5 show two reactor and separator arrangements for implementing the invention. FIG. 6 represents an embodiment of the invention with means for capturing unconverted H2S.

Figure 7 shows the X-ray diffraction pattern of the solid used in Example 1 as the initial non-stoichiometric metal sulfide. The x-axis represents the angle of deviation between the incident beam and the detector expressed in radian degree and the y-axis represents the intensity of the diffraction lines expressed in arbitrary units.

Figure 8 shows the hydrogen production over time (in min, x-axis) and depending on the type of initial iron sulphide used in a fixed bed reactor (black curve: non-stoichiometric sulfuric iron, pyrrhotite, gray curve: stoichiometric sulfuric iron, metal sulphide predominantly consisting of troilite). The ordinate axis represents the hydrogen concentration of the gases leaving the reactor in 0/0 vol. FIG. 9 represents the X-ray diffraction spectrum of the solid after exhaustion of the reaction of Example 1. The abscissa represents the deflection angle between the incident beam and the detector expressed in radian degree and the axis. ordinates represents the intensity of the diffraction lines expressed in arbitrary units.

Figure 10 shows the X-ray diffraction pattern of the solid used in Example 2 as the initial stoichiometric metal sulfide. The x-axis represents the angle of deviation between the incident beam and the detector expressed in radian degree and the y-axis represents the intensity of the diffraction lines expressed in arbitrary units.

Figure 11 shows the X-ray diffraction pattern of the solid of regenerated iron sulfide. The x-axis represents the angle of deviation between the incident beam and the detector expressed in radian degree and the y-axis represents the intensity of the diffraction lines expressed in arbitrary units.

Figure 12 shows the X-ray diffraction pattern of the yellow solid collected in the trap. The x-axis represents the angle of deviation between the incident beam and the detector expressed in radian degree and the y-axis represents the intensity of the diffraction lines expressed in arbitrary units.

Figure 13 shows hydrogen production over time (in days, abscissa) by placing a non-stoichiometric iron sulfide, pyrrhotite, in a fixed bed reactor. The ordinate axis represents the hydrogen concentration of the gases at the outlet of the reactor in% vol. Figure 14 shows hydrogen production over time (in seconds, x-axis) by placing a non-stoichiometric iron sulfide, pyrrhotite, in a circulating bed reactor. The ordinate axis represents the hydrogen concentration of the gases at the outlet of the reactor in% vol. Figure 15 shows hydrogen production over time (in hours, abscissa) by placing a non-stoichiometric nickel sulfide, NiS0, 84, in a fixed bed reactor. The ordinate axis represents the hydrogen concentration of the gases at the outlet of the reactor in% vol. Figure 16 shows hydrogen production over time (in hours, abscissa) by placing a non-stoichiometric cobalt sulfide, CoS0, 89, in a fixed bed reactor. The ordinate axis represents the hydrogen concentration of the gases at the outlet of the reactor in% vol.

The principle of the invention is based on the phase transformation reaction of a non-stoichiometric metal sulphide belonging to group VIIIB of the Mendeleev classification.

By definition, for the purposes of the present invention, a TaXb compound is said to be stoichiometric when its composition respects the valence of the elements engaged.

By definition within the meaning of the present invention, the term "non-stoichiometric compound" a compound of formula Ta + zXb or TaXb_z., Ta_zXb or TaXb +, .. Non-stoichiometric compounds have significant deviations from a stoichiometric composition. From a structural point of view, it is possible to interpret these deviations by supposing the existence of gaps or interstitials or vacancies in one of the two sub-networks of the crystal. The neutrality of the crystal can then be ensured by electronic defects. In general, non-stoichiometric compounds are Ta + zXb or TaXb_z., Ta_zXb or TaXb + z. with z or z 'corresponding to the stoichiometric difference with respect to the so-called TaXb stoichiometry composition.

For the purposes of the present invention, the term "non-stoichiometric metal sulphide" means a metal sulphide which has gaps either at the level of the metal or at the level of the sulfur. A non-stoichiometric metal sulphide according to the invention will have the formula Ma + ZSb OR MaSb_z ', Ma_ZSb or MaSb + Z' with M corresponding to a metal chosen from the metals of group VIIIB of the periodic table of Mendeleïev, S sulfur, z or z 'corresponding to the stoichiometric difference with respect to the so-called MaSb stoichiometry composition.

For the purposes of the present invention, the term "initial metal sulphide" or "non-stoichiometric metal sulphide" is intended to mean the non-stoichiometric metal sulphide which is brought into contact with the sulphurous hydrogen charge. This initial metal sulfide is a substrate for the reaction of the chemical reaction.

For the purposes of the present invention, the term "converted metal sulphide" means a metal sulphide which is produced during the reaction between the initial metal sulphide and the sulphuryl hydrogen charge. The converted metal sulfide is a product of the chemical reaction.

For the purposes of the present invention, the term "regenerated metal sulphide" means a converted metal sulphide which has undergone a regeneration step.

According to the invention, the H2S is brought into contact with a non-stoichiometric metal sulphide, said initial metal sulphide, belonging to the group VIIIB of the Mendeleev classification. During this contact, the H2S reacts with the metal sulphide and converts this metal sulphide into another metal sulphide, called a sulfide metal, with a higher sulfur content. This phase transformation is accompanied by a production of hydrogen.

The non-stoichiometric metal sulphides used in the present invention may be sulphides of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum for the elements of group VIIIB . The sulphides of nickel, iron, cobalt, rhodium or molybdenum are preferably chosen because they are cheaper.

In the iron example, non-stoichiometric iron sulphides exist in different forms. To name but a few, non-stoichiometric iron sulfides can be: mackinawite, denoted Fe1 + XS with x between 0 and 0.2 with 0 being excluded from the range; preferably x varying from 0 to 0.19 with 0 being excluded from the range; even more preferred x ranging from 0.005 to 0.17 inclusive. pyrrhotite Fe1_XS with x ranging from 0 to 0.2 with 0 being excluded from the range, preferably x ranging from 0 to 0.19 with 0 being excluded from the range; even more preferred x ranging from 0.005 to 0.17 inclusive. smythite Fei + xS4 with x between 0 and 0.2 with 0 being excluded from the range; preferably x ranging from 0 to 0.19 with O being excluded from the range; even more preferred x ranging from 0.005 to 0.17 inclusive.

Pyrrhotite, of global formula Fe1_XS is a metal sulphide having vacancies (also called gaps) metal with x being defined above. In contact with hydrogen, pyrrhotite is able to transform into pyrite and marcasite according to the following reaction: Fe1_xS + (1-2x) H2S -> (1-x) FeS2 + (1-2x) H2

In the case of other metals (other than iron), the non-stoichiometric sulphides correspond to the global formula MS, that is to say that these sulphides have vacancies in the sulfur atoms. For rhodium, cobalt and nickel x is between 0 and 0.2 with 0 being excluded from the range; preferably x ranging from 0 to 0.19 with 0 being excluded from the range; even more preferred x ranging from 0.005 to 0.17 inclusive.

The following examples serve to illustrate the invention but are in no way limiting. Indeed, the stoichiometry of this sulfurization reaction depends on the selected metal sulfide. Hydrogen production reactions for these sulfides can be for example: 3 RhSo, 889 + 1.333 H2S → Rh3S4 + 1.333 H2 NiSo, 84 + 1.16 H2S → NiS2 + 1.16 H2 3 CoS0.89 + 1.33 H2S -> Co3S4 + 1.33 H2

The initial metal sulphides may be in bulk form, i.e. pure (100% weight), or in admixture with each other. As a non-limiting example of the invention, a mixture of initial metal sulphides used in the context of the invention is a mixture of CoS0, 89 and Feo88S, or a mixture of NiS0, 84 and CoS0, 89 or any other combination metal sulphides.

The material comprising the initial metal sulphide may comprise between 0.01% and 100% by weight of initial metal sulphide, preferably between 15% and 100% by weight, preferably between 15% and 90% by weight, more preferably between 50% by weight. and 100% by weight, more preferably between 90% and 100% by weight of initial metal sulfide.

The initial metal sulfides may be supported on supports such as silicas, or aluminas, or silica-aluminas, or any other type of solid support. Solid supports such as natural or synthetic zeolites can be considered in the present invention. By way of example, mention may be made of faujasites, mordenites, zeolites X and Y. The initial metal sulphides may also be arranged on supports such as fluorinated or chlorinated aluminas, natural or synthetic clays, aluminates, silicates, titanates, spinel structures. The supported metal sulphides are obtained by the techniques known to those skilled in the art (impregnation, etc.). The metal content of the initial metal sulphides supported is between 0.01% by weight and 15% by weight, preferably between 0.01% by weight and 7% by weight, more preferably 0.01% and 5% by weight. .

The initial metal sulfides can be deposited on a material. The material comprises the support as well as compounds which have participated in the preparation of the support, such as, for example, binders, additives, diluents, pore-forming agents. By way of non-limiting example, lubricant additives may be used (stearic acid, graph, etc.), additives (starch, etc.), clay additives (montmorillonite, kaolinite, etc.) or any other known additive of the skilled person. When the initial non-stoichiometric metal sulphide is deposited on a material, the assembly consisting of the material and the initial metal sulphide preferably comprises more than 15% by weight of metal sulphide, more preferably more than 50% by weight of metal sulphide, more preferably still more than 90% by weight of metal sulfides.

The initial metal sulfides can be in solid or liquid form, in the form of powder, beads or extrudates. The invention does not require any particular restriction as to the form of the metal sulfide used.

The feedstock of the process according to the invention contains between 0.5% and 100% molar H 2 S, preferably between 1% and 100% H 2 S and even more preferably between 50% and 100% H 2 S. The feedstock of the process according to the invention may be an effluent from a natural gas treatment process. By way of non-limiting example, the natural gas treatment process may be an amine separation process (method using MDEA), an adsorption process (activated carbon, etc.). The feedstock of the process according to the invention can also come from gaseous effluents of hydrotreatment in refineries. The charge can also be H2S obtained by reaction of sulfur on coal or on coal or on any type of hydrocarbon. In another example, the feed may be an effluent from a partial redox hydrocarbon unit. The charge can be in liquid or gaseous form.

The conditions for carrying out the reaction between the initial metal sulfide and the H 2 S feed are chosen so as to produce hydrogen. In particular, it is possible to choose a reaction temperature which makes it possible to produce hydrogen.

In general, the contact between the feedstock comprising H2S and the initial metal sulphide can be carried out under the conditions of availability of the feedstock. In the case of H2S produced during the deacidification of a natural gas, the contacting between the charge comprising H2S and the initial metal sulphide can be carried out at a pressure of between 0.1 and 14 MPa, and temperature between -40 and 1000 ° C, and preferably between 0 and 700 ° C. The treatment according to the process of the invention with gaseous feeds such as refinery gases can be carried out under pressure conditions between 0.1 and 20 MPa, and temperatures between -40 ° C and 900 ° C and preferably between 20 and 700 ° C. In the case of obtaining the H2S by a cryogenic distillation process, the charge containing the H2S obtained in liquid form is brought into contact with the initial metal sulphide at a temperature of between -40 ° C. and 900 ° C. and preferably between -40 ° C and 700 ° C.

More particularly, the reaction temperature can be chosen in particular as a function, for example, of the type of initial metal sulphide used.

For the initial metal sulfide whose metal is cobalt, the temperature range of the reaction may be up to 1000 ° C, or up to a temperature below the melting point of the initial metal sulfide used or the second metal sulfide formed . Preferably, it is between 20 ° C and 1000 ° C, even more preferably 100 ° C and 600 ° C, more preferably 150 ° C and 500 ° C. Preferably, the initial metal sulphide is CoS0, 89.

In the case of the initial metal sulphide whose metal is rhodium, the hydrogen production reaction can be carried out at a temperature below 800 ° C., or even 700 ° C.

Preferably, the temperature is between 20 ° C and 800 ° C, even more preferably 50 ° C and 700 ° C, more preferably 150 ° C and 500 ° C. Preferably, the initial metal sulphide is RhSo8889

In the case of the initial metal sulphide whose metal is nickel, the hydrogen production reaction can be carried out at a temperature below 500 ° C., or even 450 ° C. Preferably, the temperature is between 20 ° C and 500 ° C, even more preferably 30 ° C and 450 ° C, even more preferably 100 ° and 450 ° C. Preferably, the initial metal sulphide is NiSo, 84.

In the case of the initial metal sulphide of which the metal is iron, the hydrogen production reaction can be carried out at a temperature below 500 ° C., or even 450 ° C. Preferably, it is between 20 ° C and 500 ° C, even more preferably 50 ° C and 500 ° C, even more preferably 100 ° and 450 ° C. Preferably, the metal sulphide is pyrrhotite.

In the case of the initial metal sulphide whose metal is molybdenum, the hydrogen production reaction can be carried out at a temperature below 800 ° C. Preferably, the temperature is between 20 ° C and 800 ° C, even more preferably 50 ° C and 700 ° C, more preferably 150 ° and 500 ° C.

Contacting the initial metal sulfide with the H2S feed can be accomplished in a variety of ways.

This contacting can be carried out in a gas-solid or liquid-solid contacting column. The initial solid metal sulfide may be attached to the column members, for example on the distributor trays or on the column packing, or used as a packing element of the column.

With reference to FIG. 1, the feedstock comprising the H2S arriving via the conduit (2) may be brought into contact with the initial metal sulphide suspended in a liquid solvent (5) contained in an enclosure. The products of the reaction and optionally the unconverted H2S are evacuated via the conduit (4). The solvent containing the converted metal sulphide is discharged through line (3).

In another embodiment of the invention, the placing in contact can be carried out in beds. With reference to FIG. 2, the contacting can also be carried out by scanning the effluent comprising the H2S arriving via the conduit (8) in a reactor (6) containing the initial metal sulphide, arranged in the form of fixed beds. (7). The gaseous effluent comprising the hydrogen produced by the reaction between the H2S and the metal sulfide is removed from the reactor (6) via the conduit (9).

In another embodiment of the process, the "moving bed" technique may also be employed: the feed comprising H 2 S is contacted in a reactor with the initial metal sulfide in the form of powder or particles. The circulation of the charge makes it possible to drive the particles, maintaining a homogeneous and disjoint distribution of the initial metal sulphide particles.

According to another embodiment, it is possible, if desired, to implement the invention in a particular device that allows the removal of hydrogen as it is formed. This device is not mandatory. Examples of devices for removing hydrogen during the reaction are shown below. According to one embodiment described with reference to FIG. 3, a membrane reactor (10) is used. The initial metal sulfide (11) is contained in an enclosure (12) having one or more walls consisting of a membrane permeable to hydrogen and preferably impermeable to H2S. The charge comprising H2S is introduced into the chamber in order to be in contact with the initial metal sulphide. In the contactor, a carrier gas is also introduced through the conduit (17), for example water vapor. This carrier gas scans the outer surface of the membrane constituting the enclosure (12) in order to evacuate the hydrogen produced inside the enclosure. The hydrogen transfer from the interior of the enclosure to the outside is notably caused by the difference in hydrogen concentration and by the pressure difference on either side of the hydrogen-permeable membrane. Thus, the hydrogen produced inside the chamber by the reaction between the H2S and the initial metal sulfide is carried by the carrier gas and discharged through the conduit (18). The gaseous effluent depleted in H2S and enriched with water is removed from the enclosure (12) via the conduit (16). Thus, the use of the membrane reactor makes it possible to evacuate the hydrogen as soon as it is formed.

According to the invention, it is possible to use different types of membrane, for example a membrane of the gas permeation type, a pervaporation type membrane, an organic membrane, an inorganic membrane, a dense membrane, a porous or microporous membrane, a polymer membrane, a composite membrane made of polymer and at least one inorganic compound, a molecular sieve film-based membrane, a film-based membrane formed from silicate, aluminosilicate, aluminophosphate, silicoaluminophosphate, metalloaluminophosphate, molecular sieves, stanosilicates or a mixture of at least one of these two types of constituents, a film-based membrane formed of zeolites, membrane based on zeolites of MFI or ZSM-5 type, native or having been exchanged with H + ions; Na +; K +; Cs +; It +; Ba + or ions of group VIIIB elements, a LTA type zeolite membrane, a porous membrane impregnated with a liquid, a porous membrane impregnated with a polymer. If the reactor temperature is below 150 ° C, glassy polymers or any glassy polymer mixture with molecular sieving properties in the form of dense films can be selected. In a non-exhaustive manner, polymers of the family of sulfones, polyethersulfones, polyimides, polyamides or acetates are suitable for this type of separation. The presence of fluorine atoms in the polymer chain can also improve the performance of these polymers because the presence of this element contributes to the stiffening of the polymer chains and generally improves the chemical stability of the polymers. In general, it is preferred to choose a polymer whose glass transition temperature is greater than 150 ° C, or even 200 ° C or 250 ° C. Indeed, a high value of this parameter is most often synonymous with increased molecular sieving properties. The membranes employing this type of polymeric material can be operated in a mode called "gas permeation" or in a mode called "pervaporation". If the reaction takes place at higher temperatures, that is to say between 250 ° C and 500 ° C, a dense membrane based on an intimate alloy of palladium and copper at respective mass contents of 60% and 40% may be suitable for the continuous separation of hydrogen from sulfurous hydrogen. Indeed, this membrane offers increased resistance to the presence of hydrogen sulphide, unlike native palladium or standard palladium / silver alloys. In addition, the thermal range 250 ° C-500 ° C corresponds to an optimum compromise hydrogen permeability / mechanical strength of the Pd-Cu alloy (60-40). Finally this membrane offers the unique advantage of being infinitely selective with hydrogen since only hydrogen can diffuse in this alloy in the form of hydrides.

With reference to FIG. 4, the present invention is implemented by means of a processing chain comprising a series alternation of reactors R1, R2 and membrane separation stages M1, M2. The number of reactor alternations and separation stages can be chosen as a function of the gaseous effluent to be treated. In reactors R1 and R2, the feedstock comprising H2S arriving via line (20) is contacted with initial metal sulfide. These reactors may be of the type of the reactors described with reference to FIGS. 1, 2 and 3. Then after each of the reactors R1 and R2, the hydrogen is separated from the effluent by means of a separation in the separation stages M1 and M2. The membranes used in MI and M2, permeable to hydrogen and preferably impermeable to H2S, may be those described above. The gaseous effluent depleted of H2S is removed from M1 to be introduced into R2 or removed from M2 by the conduit (21). In the case of a regeneration of the transformed metal sulphide, it is then very easy to isolate one of the reactors R1, R2 from the entire treatment chain in order to achieve the regeneration, while continuing the production process. of hydrogen with the other elements of the treatment chain. In addition, the heat produced during the regeneration of the transformed metal sulfide contained in the reactor does not affect the membranes of the separation stages.

Referring to Figure 5, the feedstock comprising H2S is introduced into the reactor R through the conduit (30) and discharged through the conduit (31). The continuous extraction of hydrogen is effected by means of a recycle loop of a fraction of the reaction effluent which is depleted of hydrogen by means of the membrane separation stage M and then reinjected at the inlet of the reactor R: part of the gas leaving R is introduced into M via the conduit (32), the hydrogen-depleted gas leaving M is recycled to the inlet of R through the conduit (33). The coupling between the membrane separation stage M and the reactor R, leading to the increase in the productivity of the reactor R by unbalancing the reaction mixture, is particularly efficient in the case where the flow rate of the recycle (32) is greater than flow of the inlet gas through the conduit (30). In M, the hydrogen is separated by means of a membrane, for example a membrane as described above, permeable to hydrogen and preferably impermeable to H2S. In a manner similar to the embodiment described with reference to FIG. 4, the reactor R can be isolated from the membrane separation stage M to be regenerated without damaging the membrane material.

According to another embodiment, it is possible to capture the H2S that has not been converted in the process according to the invention. Capture is effected by means well known to those skilled in the art. By way of nonlimiting example, a capture means may be the use of a solvent such as primary, secondary or tertiary alkanolamines. Contacting the unconverted H2S with the solvent can be carried out conventionally in one or more co-current or countercurrent contact columns or in membrane contactors. The unconverted H2S captured can be totally or partially recycled and serve as a feed for the process according to the invention. With reference to FIG. 6, the charge comprising H2S is introduced into the reactor R via the conduit (40) and brought into contact with the initial metal sulphide. The reactor may be of the reactor type described with reference to FIGS. 1, 2 or 3. The effluent is evacuated via the conduit (41). Unconverted H2S is separated from the effluent by solvent capture. All or part of the effluent to be treated arrives via the conduit (42) and is introduced into the contacting column (Cl). The capture solvent arrives via the conduit (43). The capture solvent is chosen for its ability to absorb H2S. This solvent may be an absorption solution formed of at least one or more organic compounds and / or one or more compounds having the ability to react reversibly with H2S. These compounds are well known to those skilled in the art and may be for example and without limitation amines (primary, secondary or tertiary cyclic or nonaromatic or not), alkanolamines, amino acids ... In the column Cl the solvent captures and absorbs the unconverted H2S contained in the effluent. The flow rich in H2 is removed from the column C1 by the conduit (44). The solvent charged with H2S is evacuated via the conduit (45) and is introduced into the column C2 to be regenerated. In general, the regeneration is carried out by distillation of the solvent. At the bottom of the column C2, an H2S-depleted liquid solvent is obtained and at the top of the column a gaseous effluent containing H2S. The regeneration of the solvent can be carried out conventionally in one or more columns which can be lined with perforated trays, with valves or with caps. These columns can also be bulk packing type or structured. The regenerated solvent obtained at the bottom of the column C2 is evacuated via the conduit (46) and can be reintroduced into the column via the conduit (43). The gaseous effluent containing H2S is evacuated via the conduit (47) and can be totally or partially recycled in the reactor R.

According to one embodiment, the method according to the invention may comprise a regeneration step after the reaction step of the initial metal sulfide with H 2 S. The regeneration can be carried out by heat treatment of the metal sulphide converted in the presence or absence of a gas. An inert gas (nitrogen, argon, helium, etc.), pure air or a mixture with another gas, oxygen or diluted with another gas can be used. This calcination is carried out at pressures of between 0.1 and 20 MPa, but preferably between 0.1 and 100 MPa, at temperatures of between 20 and 1000 ° C. and preferably between 200 and 900 ° C. The principle of regeneration is based on the phase transformation reaction of metal sulphide, belonging to group VIIIB of the Mendeleev classification, to initial metal sulphide and sulfur.

According to a non-limiting example of the invention, in the case of pyrrhotite, the operation of the process can be schematized according to the following sequences of reactions: hydrogen production: Fe1_XS + (1-2x) H2S -> (1-x ) FeS2 + (1-2x) H2 regeneration of pyrrhotite according to the reaction below: (1-x) FeS2 -> Fe1_XS + ((1-2x) / 8) S8

The sulfur evolved during the step is in gaseous form and can be recovered in liquid form by cooling to a temperature below 444 ° C and / or in solid form by cooling to a temperature below 112 ° C.

The regeneration can be carried out simply by heating the solid at temperatures between 20 and 1000 ° C and preferably between 200 ° C and 1000 ° C.

Regeneration can be performed by injecting an inert gas onto the solid. The presence of an inert gas makes it possible to increase the efficiency of the regeneration reaction by promoting the elimination of sulfur, which is in the gaseous state during the reaction.

The gaseous sulfur or the gaseous effluent containing the sulfur in the gaseous state is then cooled by any apparatus (exchanger, separator, etc.). This allows the condensation of sulfur in the liquid (or solid) state so that it can be recovered for recovery.

These reactions are given for information only and are not limiting. Indeed, the stoichiometries of these reactions depend on the nature of the metal sulphide. The regeneration makes it possible to convert the metal sulphide into an initial metal sulphide which can be reused for the hydrogen synthesis reaction. In the case where it is desired to improve the yield of the hydrogen production reaction by extracting one of the products of the reaction, in particular hydrogen, by means of a membrane, it is preferable to geometrically dissociate the reaction stage or stages of the membrane separation stage (s) in order to be able to regenerate the catalytic solid without causing possible damage. to membranes due to calcination. The contacting means of FIGS. 4 and 5 associating membrane and reactor make it possible to carry out the regeneration by isolating the membrane stages by means of pipes.

The examples given below make it possible to illustrate the invention but are in no way limiting. They show the importance of the crystalline form of the iron sulphide used.

Example 1 (according to the invention): In this example, the reaction is carried out using, as initial metal sulphide, a solid consisting of pyrrhotite of formula Fe1_XS. The solid obtained is characterized by X-ray diffraction via a Bragg-Brentano type powder diffractometer in the 6-6 configuration. The spectrum obtained is shown in FIG. 7. This spectrum is characteristic of pyrrhotite. A quantity of 6 grams of this finely ground solid is loaded into a fixed bed reactor. The solid is heated to 250 ° C. A charge consisting of pure H 2 S, at a total pressure of 0.4 MPa, is sent in contact with the solid at a 55 hr hourly volumetric speed (the hourly volumetric rate is the hourly liquid flow in volume per unit volume catalyst). The gases leaving the reactor are analyzed by gas chromatography; they consist of an H2S mixture and hydrogen. The results obtained are shown in FIG. 8. It can be seen that the synthesis of hydrogen using pyrrhotite as initial metal sulphide extends over a period of 3500 min (black curve). After exhausting the reaction, ie no more hydrogen is produced, the solid is cooled, discharged and analyzed by X-ray diffraction. The X-ray diffraction spectrum of the final solid (Figure 9) shows that the solid after reaction consists of a mixture of pyrite and marcasite FeS2 formula. Example 2 (Comparative): The same experimental conditions of the preceding example are repeated but with another solid, the X-ray diffraction spectrum of which is shown in Figure 10. From this figure, it can be seen that the solid of Example 2 consists mainly of troilite, of formula noted FeS, and a small amount of pyrrhotite. The troilite is an iron sulphide containing only 36.5% sulfur atomic percentage, it is a stoichiometric sulfide. 6 grams of this finely ground solid are loaded into a fixed bed reactor. The solid is heated to 250 ° C. A charge consisting of pure H 2 S, at a total pressure of 0.4 MPa, is sent into contact with the solid at an hourly volumetric rate of 55 h -1, under the same operating conditions as those of Example 1. In the same manner, the gases leaving the reactor, consisting of an H2S mixture and hydrogen, are analyzed by gas chromatography. The results obtained are shown in FIG. 8. It can be seen that the synthesis of hydrogen using a metal sulphide consisting predominantly of troilite extends over a period of 1900 min (gray curve).

Example 1 and Example 2 show that the amount of hydrogen produced by the solid consisting solely of Fe1_XS pyrrhotite is much greater than that produced by the solid consisting mainly of FeS troilite and this for a period twice as long.

Example 3 After exhaustion of the reaction, the solid from Example 1 is analyzed by X-ray diffraction. Its spectrum (FIG. 9) shows that it consists of pyrite and marcasite. This solid is placed in a quartz reactor under a nitrogen flow rate of 30 Nl / h at atmospheric pressure. The reactor is heated in a tubular furnace. At the outlet of the reactor, a heated line brings the vapors leaving the reactor in a glass trap containing glass beads. This trap is at room temperature. From 350 ° C, vapors begin to appear at the outlet of the reactor. Between 400 ° C and 700 ° C the yellow vapors condense in a glass trap into a yellow solid. After 4 hours of heating at 600 ° C, the heating is cut off, the solid remaining in the reactor is analyzed by X-ray diffraction (Figure 11). This spectrum shows that the discharged solid consists exclusively of Fe1_xS pyrrhotite. The solid has returned to its original state. The yellow solid collected in the trap is also analyzed by X-ray diffraction (FIG. 12), which concludes with the shape of sulfur S8.

Example 4: 20 grams of pyrrhotite are placed in a reactor heated to 250 ° C. Pure H2S is injected at 4 bars (1 bar = 105 Pa) of pressure with an hourly volumetric velocity of 5.5 h ". The gases leaving the reactor, consisting of an H2S mixture and hydrogen, are analyzed by gas chromatography as a function of time. The results obtained are shown in FIG. 13. The hydrogen concentration of the gases leaving the reactor is 40% vol. This hydrogen content remains stable at 40% by volume (or molar) for 5.4 consecutive days. The hydrogen content remained above 30% by volume for 8 consecutive days.

Example 5 3.05 grams of pyrrhotite are placed in a circulating bed pilot unit to study the hydrogen yield under conditions different from the fixed bed. The reaction portion is heated to 330 ° C under 4 bar H 2 S. The gases leaving the reactor, consisting of an H2S and hydrogen mixture, are analyzed by gas chromatography as a function of time. The results obtained are shown in FIG. 14. The hydrogen concentration of the gases leaving the reactor is 90% by volume.

Example 6: A mass of 5.84 g of nickel sulfide NiS0.84 is placed in a fixed bed reactor. Pure H2S is sent under a pressure of 4 bar with a hourly volume velocity of 100 h -1. This reactor is heated between 190 ° C and 400 ° C in stages at different temperatures: 190 ° C, 230 ° C, 270 ° C, 310 ° C, 350 ° C, 380 ° C. The gases leaving the reactor, consisting of a mixture of H 2 S and hydrogen, are analyzed by gas chromatography as a function of time. The results obtained are shown in FIG. 15. The hydrogen concentration of the gases leaving the reactor increases from 5 to 45% by volume between 190 and 380.degree.

Example 7: A mass of 6.02 g cobalt sulfide CoS0.89 is placed in a fixed bed reactor. Pure H 2 S is sent under a pressure of 4 bar with an hourly space velocity of 16 h -1 This reactor is heated to 150 ° C. The gases leaving the reactor, consisting of a mixture of H 2 S and H 2 The results obtained are shown in FIG. 16. The hydrogen concentration of the gases leaving the reactor is 80% by volume for at least 3 hours at 150.degree.

Claims (16)

REVENDICATIONS1. Process for producing hydrogen from a CLAIMS1. A process for producing hydrogen from a feedstock comprising hydrogen sulphide, wherein said feedstock is contacted with a material comprising at least one initial metal sulphide to produce hydrogen and a converted metal sulphide said initial metal sulfide being a non-stoichiometric sulfide of a Group VIIIB metal of the Mendeleev Periodic Table. The process of claim 1, wherein the metal of said initial metal sulfide is selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium and nickel. 3. A process according to claim 1, wherein the metal of said sulfide is iron and in which operation is carried out at a temperature of between 20 ° C and 500 ° C, preferably between 50 ° C and 500 ° C, even more preferred 100 ° C and 450 ° C. 4. The method of claim 3, wherein when the metal of said initial metal sulfide is iron, the metal sulfide being selected from the group consisting of mackinawite, pyrrhotite and smythite. 20 5. The process according to claim 4, wherein the initial metal sulfide is pyrrhotite and wherein operation is carried out at a temperature of between 100 ° C and 450 ° C. 6. The method of claim 1, wherein the metal of said sulfide is rhodium and wherein one operates at a temperature between 20 ° C and 800 ° C, more preferably between 50 ° C and 700 ° C, even more preferred between 150 ° C and 500 ° C. 7. The method of claim 1, wherein the metal of said sulfide is cobalt and wherein one operates at a temperature between 20 ° C and 1000 ° C, more preferably between 100 ° C and 600 ° C, even more preferred between 150 ° C and 500 ° C. 30 8. Process according to claim 1, in which the metal of said sulphide is nickel and in which operation is carried out at a temperature of between 20 ° C. and 500 ° C., more preferably between 30 ° C. and 450 ° C., and even more so. preferred between 100 ° C and 450 ° C. 9. Method according to one of claims 1 to 8, wherein the effluent 35 is contacted with the metal sulfide with one of the following means: a contacting column, a fixed bed reactor, a reactor moving bed. 10. Method according to one of claims 1 to 8, wherein the initial metal sulfide is contained in an enclosure comprising at least one membrane wall permeable to hydrogen and causes the migration of hydrogen through the membrane by pressure difference or difference in hydrogen concentration. 11. The method according to one of claims 1 to 8, wherein after the chemical reaction step, a separation step is carried out in which the hydrogen is separated by means of a membrane permeable to hydrogen to obtain a effluent depleted in hydrogen and a flow rich in hydrogen. 12. The method of claim 11, wherein at least two sequences are carried out comprising the chemical reaction step followed by the separation step. 13. Method according to one of claims 10 to 12, wherein the membrane comprises a dense film comprising a polymer whose glass transition temperature is greater than 150 ° C or a dense film comprising palladium and copper. 14. A method according to one of claims 1 to 8, wherein is carried out, after the chemical reaction step, a step of capturing unconverted H2S to obtain a hydrogen-rich stream. 15. Method according to one of claims 1 to 14, wherein the transformed metal sulfide is regenerated by calcination at a calcination temperature of between 100 and 1000 ° C. 16. Process according to one of Claims 1 to 14, in which the transformed metal sulphide is regenerated by calcination in the presence of an inert gas.